1. Field of the Invention
The present invention relates to an apparatus and method for servo control of an optical disk drive, and more particularly, but not by way of limitation, to servo control apparatus and method that adjusts the rotation speed of an optical disk in consideration of the amount of axial vibration of the optical disk.
2. Description of the Related Art
Shown in FIG. 1 is a general optical disk reproducing apparatus, comprising an optical pickup 2 for reproducing recorded signals from an optical disk 1, an R/F unit 3 for equalizing and shaping the RF signals reproduced by the optical pickup 2, a sync clock generator 7 for creating a clock signal synchronized with the binary data outputted from the R/F unit 3, a digital signal processing unit 4 for processing the binary data stream received from the R/F unit 3 to retrieve digital data using the synchronization clock, an interface unit 5 for connecting the retrieved digital data to a PC, a sled motor 11 for moving the optical pickup 2, a spindle motor 12 for rotating the optical disk 1, a driver 8 for driving the sled motor 11 and the spindle motor 12, a servo unit 6 for controlling the optical pickup 2 and the driver 8, a microcomputer 9 for supervising overall operation of the servo unit 6 and the digital signal processing unit 4, and a memory 10 for storing data necessary for the microcomputer 9.
The servo control operation of the general optical disk reproducing apparatus is as follows.
Once the optical disk 1 is inserted into a disk tray, which is a part of the optical disk reproducing apparatus mechanism, the optical disk 1 is clamped by a clamping device. Then, controlled by the servo unit 6, the driver 8 provides the spindle motor 11 with electric current, thereby rotating the optical disk 1.
To reproduce signals recorded on the optical disk 1, the optical pickup 2 with a laser diode and photo diodes installed in it, forms a laser beam spot on the recording layer of the optical disk 1 by irradiating a laser beam from the laser diode. The laser beam reflected from the optical disk 1 is collected by the photo diodes and converted into electric signals. The R/F unit 3 equalizes and shapes the electric signals to produce binary data and the digital signal processing unit 4 performs the processing of the binary data to retrieve original data. The synchronization clock needed for the digital signal processing unit 4, synchronized with the binary data from R/F unit 3, is provided by the sync clock generator 7.
Using the synchronization clock, the digital signal processing unit 4 retrieves original digital data from the binary data outputted by the R/F unit 3.
The basic role of the sled motor 11 is to move the optical pickup 2 in the radial direction. Controlled by the servo unit 6, the sled motor 11 moves the optical pickup 2 rapidly in the radial direction in the track search mode for locating a desired track. Also controlled by the servo unit 6, the spindle motor 12 rotates the optical disk 1 with a required rotation speed.
After the optical disk 1 is inserted into the disk tray and clamped by the clamping device, the microcomputer 9 controls the servo unit 6 so that the driver 8 increases the input voltage to the spindle motor 11. As the rotation speed of the optical disk 1 increases, the data transfer rate of the optical disk reproducing apparatus also becomes higher.
For read-out of recorded data with a high rotation speed, high-accuracy tracking and focusing control is required. In the instance where the axial vibration of the optical disk caused by imperfect disk manufacturing process, disk clamping error, or disk tilt exceeds a certain limit, tracking and focusing control may yield large errors and thus normal data read-out becomes impossible, which is a major obstacle to high-speed rotation optical disk reproducing apparatus.
It is an object of the present invention to provide a servo control apparatus and method that provides stable data read-out capability by adjusting the allowable maximum disk rotation speed by measuring the amount of axial vibration of a rotating optical disk.
The servo control apparatus in accordance with the present invention comprises driver means for rotating the optical disk, detection means for detecting the amount of axial vibration of the rotating optical disk, and control means for controlling the rotation speed of the optical disk based upon the detected amount of disk axial vibration.
According to the servo control apparatus and method of the present invention, if an optical disk is inserted into a disk tray, the amount of disk axial vibration is measured from a center error signal by rotating the optical disk at a low speed with only focusing control activated. The allowable maximum rotation speed of the optical disk is limited based on the measured amount of disk axial vibration.